For the applications envisaged it is important that the equipment should be compact and light in weight; be rugged and simple to use, especially by unpractised users; and be reliable and self-adapting to the requirements of different users and different operational circumstances.
Breathing equipment for these purposes essentially comprises a suitable self-contained source of breathable gas such as clean air stored at high pressure in a suitable vessel; and means for delivering this breathing gas at a suitable pressure and in required quantities to a point of use such as a breathing mask: that is to say, the essential components correspond with those of a conventional, self-contained breathing apparatus, the means : for delivery of breathing gas at a required pressure and in required quantities typically comprising a pressure-regulator and suitable flow-control devices that may include a demand valve. However, whereas conventional self-contained breathing apparatus is typically intended for use by trained users practised in its use and capable, therefore, of using provided adjusting means to regulate gas delivery, the equipment to which the invention is directed needs to be self-regulating and self-adapting without the necessity of making any adjustments. Ideally, moreover, it should operate to mitigate the potential dangers to a user arising from misuse, e.g. due to inexperience.
The different lung capacities of individuals affect the rate of air consumption at maximum breathing rates such as occur when the individual is engaged in strenuous physical activity or is subjected to high general stress levels. However the air consumption rate necessary to sustain life is in general substantially less than the maximum corresponding with unrestrained breathing and in many circumstances a restraint on breathing rate is desirable to prevent hyperventilation and its undesirable physiological consequences. Indeed, if there is restraint upon the rate of air consumption not only is hyperventilation prevented but a calming influence is exerted. Accordingly while the lung capacities of individuals may differ significantly, their air consumption rates at a life-sustaining level are remarkably similar. The present invention utilises this phenomenon.